Energetic fluoronitro prepolymer

ABSTRACT

Hydroxy-terminated poly(2-fluoro-2,2-dinitroethyl) polynitroorthocarbonaterepolymers of the formula ##STR1## which are prepared by reacting bis(2-fluoro-2,2-dinitroethyl)dichloroformal with a diol of the formula ##STR2## wherein n&gt;1, and wherein W, X, Y, and Z vary independently and are F or NO 2 , and wherein A is --CH 2  --, --CH 2  CH 2  --, --CH 2  CH 2  CH 2  --, --CF 2  --, --CF 2  CF 2  --, --CF 2  CF 2  CF 2  --, --CF 2  CF 2  CF 2  CF 2  --, --CH 2  OCH 2  --, --CH 2  OCH 2  OCH 2  --,--CH 2  OCF 2  OCH 2  --, or --CH 2  N(NO 2 )CH 2  --. These prepolymers are reacted with curing agents (e.g., polyisocyanates) to form energetic polymeric binders.

BACKGROUND OF THE INVENTION

This invention relates to polymers and more particularly to energeticpolymers which are useful as binders in propellants and explosives.

At the present time non-energetic binders are used for propellants andexplosives. Energetic plasticizers are frequently combined with thesebinders to increase the energy. Unfortunately, the amounts of energeticplasticizer needed result in reductions in important properties such astensile strength and elongation.

It would be desirable therefore to reduce the amounts of energeticplasticizers needed in explosive and propellant binders and thus improvephysical properties such as tensile strength and elongation.

SUMMARY OF THE INVENTION

Accordingly, an object of this invention is to provide new polymers.

Another object of this invention is to provide new high energy polymers.

A further object of this invention is to provide polymers having a highconcentration of stable, high energy 2-fluoro-2,2-dinitroethyl groups.

Yet another object of this invention is to provide means of increasingthe energy content of binders without sacrificing tensile strength andelongation.

A still further object of this invention is to provide a new method ofsynthesizing energetic polymers.

These and other objects of this invention a achieved by providinghydroxy-terminated poly(2-fluoro-2,2-dinitroethyl)polynitroorthocarbonates prepolymers of the formula ##STR3## whereinn>1, and wherein W, X, Y, and Z vary independently and are F or NO₂, and--A--is --CH₂ --, --CH₂ CH₂ --, --CH₂ CH₂ CH₂ --, --CF₂ --, --CF₂ CF₂--, --CF₂ CF₂ CF₂ --, --CF₂ CF₂ CF₂ CF₂ --, --CH₂ OCH₂ --, --CH₂ OCH₂OCH₂ --, --CH₂ OCF₂ OCH₂ --, or --CH₂ N(NO₂)CH₂ --. These compounds areprepared by reacting bis(2-fluoro-2,2dinitroethyl)dichloroformal with adiol of the formula ##STR4## wherein W, X, Y, Z, and -A- are as definedabove. These prepolymers react with polyisocyanates (functionality2.0-3.0)to form energetic, rubbery polymeric binders.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The prepolymers of this invention are energetic hydroxy-terminatedpoly(2-fluoro-2,2-dinitroethyl) polynitroorthocarbonates prepolymers ofthe general formula ##STR5## which are prepared by reactingbis(2-fluoro-2,2dinitroethyl)dichloroformal, ##STR6## with a diol of thegeneral formula ##STR7## wherein n>1, and wherein W, X, Y, and Z varyindependently and are each F or NO₂, and A represents a stable,nonreactive, preferably energetic linkage which will be described later.It is critical for the formation of stablepoly(2-fluoro-2,2-dinitroethyl) polynitroorthocarbonates that W, X, Y,and Z each be a very strong electronegative fluoro or nitro group. Inother words, the carbon atoms beta to the terminal hydroxy groups musteach contain two of these strongly electronegative groups. Thus, thediols used in this invention will contain only --CF₂ CH₂ OH--,--CF(NO₂)CH₂ OH--, and --C(NO₂)₂ CH₂ OH-- end groups. Preferably the twoend groups on the diol will be identical (W equal to Y and X equal toZ). The general formula for these preferred polyfluorodinitroethylpolynitroorthocarbonates is ##STR8## wherein n>1 and the general formulafor the corresponding diol starting material is ##STR9## wherein Y and Zvary independently and are each F or NO₂.

As stated before, -A- may represent any one of a number of linkagesprovided that it is stable and is nonreactive under the conditions ofthe polymerization process. For example -A- may contain --CH₂ --,--CHF--, --CF₂ --, --CH(NO₂)--and --C(NO₂)₂ units. --A-- may alsocontain oxygen in the form of ether (e.g., --CH₂ OCH₂ --, --CF₂ OCF₂ --,etc.) or formals (e.g., --CH₂ OCH₂ OCH₂ --, --CH₂ OCF₂ OCH₂ --, etc.)units. However, unstable oxygen groups such as peroxides (--CH₂--O--O--CH₂ --) are excluded. Oxygen in a reactive form such as--CH(OH)-- is also excluded from --A--. Additionally, nitrogen may bepresent in the backbone of --A--. However, --NH-- contains a reactivehydrogen and therefore is not desirable; on the other hand, --N(NO₂)--is stable, energetic, and nonreactive and therefore suitable.

Preferably, --A-- can be --CH₂ --, --CH₂ CH₂ --, --CH₂ CH₂ CH₂ --, --CF₂--, --CF₂ CF₂ --, --CF₂ CF₂ CF₂ --, --CF₂ CF₂ CF₂ CF₂ --, --CH₂ OCH₂ --,--CH₂ OCH₂ OCH₂ --, --CH₂ OCF₂ OCH₂ --, or --CH₂ N(NO₂)CH₂ --.

The following are examples of the diols which may be reacted withbis(2-fluoro-2,2-dinitroethyl)dichloroformal to form thehydroxy-terminated polyfluorodinitroethyl polynitroorthocarbonateprepolymers of this invention:

HOCH₂ C(NO₂)₂ CH₂ OCH₂ OCH₂ C(NO₂)₂ CH₂ OH,

HOCH₂ CF(NO₂)CH₂ OCH₂₀ qH₂ CF(NO₂)CH₂ OH,

HOCH₂ C(NO₂)₂ CH₂ OCF₂ OCH₂ C(NO₂)₂ CH₂ OH,

HOCH₂ C(NO₂)₂ CH₂ C(NO₂)₂ CH₂ OH,

HOCH₂ C(NO₂)₂ CH₂ CH₂ C(NO₂)₂ CH₂ OH,

HOCH₂ C(NO₂)₂ CH₂ CH₂ CH₂ (NO₂)₂ CH₂ OH,

HOCH₂ C(NO₂)₂ CH₂ OCH₂ C(NO₂)₂ CH₂ OH

HOCH₂ C(NO₂)₂ CH₂ N(NO₂)CH₂ C(NO₂)₂ CH₂ OH,

HOCH₂ CF₂ CF₂ CF₂ CH₂ OH, and

HOCH₂ CF₂ CF₂ CF₂ CF₂ CH₂ OH.

Note that long hydrocarbon chains, --(CH₂)n--, are undesirable becausethey substantially reduce the energy content of the polymer. On theother hand, polyfluorohydrocarbon and polynitrohydrocarbon chains arepreferred because of their energy content.

Note that the -A- linkage in the diols is preferably a straight chain asthis will produce a more flexible propellant binder.

Equimolar amounts of the diol andbis(2-fluoro-2,2-difluoroethyl)dichloroformal can be used, butpreferably an excess of the diol is used to assure that the prepolymerproduct will be hydroxy-terminated. The molar ratio of diol tobis(2-fluoro-2,2-dinitroethyl)dichloroformal is from 1:1 to 2:1 andpreferably from 1.33:1 to 1.50:1.

Preferably the average molecular weight of the hydroxyterminatedpoly(2-fluoro-2,2-dinitroethyl) polynitroorthocarbonate prepolymer isfrom 1,000 to 10,000. As the molar ratio of diol tobis(2-fluoro-2,2dinitroethyl)dichloroformal is increased, the averagemolecular weight of the prepolymer produced decreases.

The polymerization reaction between a diol and thebis(2-fluoro-2,2-dinitroethyl)dichloroformal can be run without asolvent by melting the starting materials. However, it is safer and thuspreferable to use a solvent. Preferred among the solvents are thechlorohydrocarbons such as methylene chloride, 1,2-dichloroethane,1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,2,2-tetrachloroethane,and chloroform, with chloroform being the preferred solvent.Nitromethane can also be used as the solvent.

The reaction temperature is preferably from about 50° C. to about 100°C. and more preferably from 60° C. to 65° C.

Preferably a rapid stream of nitrogen is passed through the reactionmixture to remove hydrogen chloride which is generated by the reactionbetween the diol and bis(2-fluoro-2,2-dinitroethyl)dichloroformal. It isadvantageous to collect and titrate the evolved hydrogen chloride todetermine and confirm the extent of reaction.

Crude poly(2-fluoro-2,2-dinitroethyl)polynitroorthocarbonate material isobtained either by solvent evaporation or by decantation of thesupernatant liquid from the cooled reaction mixture. Purified materialis obtained by extracting the low molecular weight impurities from thecrude material with suitable solvents and/or solvent combinations. Forexample, a chloroform or a mixture of a few percent (˜2%) of methanol inchloroform will work.

The purified hydroxy-terminated poly(2-fluoro-2,2dinitroethyl)polynitroorthocarbonate prepolymers can be reacted with suitablematerials to produce energetic, plastic binders from explosives andpropellants. For example, as illustrated by Examples 4 and 6, theseprepolymers may be cured with polyisocyanates to produce rubberypolymers. Organic polyisocyanate which may be used in this inventioninclude aromatic, aliphatic and cycloaliphatic diisocyanates, as forexample: 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylenediisocyanate, 1,5-naphthylene diisocyanate, 4,4'-biphenylenediisocyanate, p,p'-methylene diphenyl diisocyanate, 1,4-tetramethylenediisocyanate, 1,6-hexamethylene diisocyanate, 1.10-decamethylenediisocyanate, 1,4-cyclohexylene diisocyanate,4,4'-methylene-bis-cyclohexyl isocyanate), 1,5-tetrahydronaphthylenediisocyanate, and polymethylenepolyphenylisocyanate (PAPI), isophoronediisocyanate, and N,N'N"-trisisocyanatohexybiuret. Mixture ofdissocyanates may also be used. Preferred polyisocyanates are2,4-toluene diisocyanate, polymethylpolyphenylisocyanate (PAPI), andN,N'N"-trisisocyanatohexylbiuret. The polyisocyanate is used in anamount sufficient to supply from about 0.8:1 to about 1.5:1 butpreferably from 1:1 to 1.2:1 isocyanate functional groups for eachhydroxy functional group.

The general nature of the invention having been set forth, the followingexamples are presented as specific illustrations thereof. It will beunderstood that the invention is not limited to these examples but issusceptable to various modifications that will be recognized by one ofordinary skill in the art.

EXAMPLES

Examples 1 and 2 illustrate methods by which thebis(2-fluoro-2,2-dinitroethyl)dichloroformal starting material can beprepared. These examples are taken from U.S. patent application Ser. No.256,462 which was filed on Mar. 30, 1981, by William H. Gilligan andwhich now is under a D-10 order.

Example 1

Bis(2-fluoro-2,2-dinitroethyl)dichloroformal

To a solution of 10.0g (28.6 mmol) of bis(2-fluoro-2,2dinitroethyl)thionocarbonate in 50 ml of freshly distilled. sulfuryl chloride wasadded 4.0 ml of titanium tetrachloride. The solution was then refluxedfor 5 days. Excess sulfuryl chloride and titanium tetrachloride werethen removed in vacuo at a bath temperature of 50° C., The solid residuewas recrystallized from chloroform to give 7.91g (71%) ofbis(2-fluoro-2,2-dinitroethyl)dichloroformal as colorless crystals, mp57°-58° C.

H - NMR (CDCl₃ /TMS) δ (ppm) - d, 5.02.

Calc. for C₅ H₄ Cl₂ F₂ N₄ O₁₀ : C, 15.44; H, 1.04;

Cl, 18.23; F, 9.77; N, 14.40

Found: C, 15.46; H, 1.05; Cl, 18.40; F, 9.98; N, 14.11.

Example 2

Bis(2-fluoro-2,2-dinitroethyl)dichloroformal

Gaseous chlorine was slowly passed into a stirred slurry of 21.0 g(0.067 mol) of bis(2-fluoro-2,2dinitroethyl)thionocarbonate in 100 ml ofdry carbon tetrachloride and 10 ml of dry trifluoroethanol for 4.5 hoursat the end of this period the slurry had changed into a clearorange-colored solution. After standing overnight, volatiles wereremoved on a rotovac and the solid residue was recrystallized fromchloroform to give 19.33 g (83%) ofbis(2-fluoro-2,2-dinitroethyl)dichloroformal, m.p. 57°-8° C.

The bis(2-fluoro-2,2-dinitroethyl)thiocarbonate used in examples 1 and 2can be prepared according to the method disclosed in example 1 of U.S.Pat. No. 4,172,088, entitled"Bis(2-Fluoro-2,2-dinitroethyl)thionocarbonate and a method. ofPreparation," which issued on Oct. 23, 1979, to Angres et al.

Example 3

To a three-necked, round bottomed flask equipped with a nitrogen inlet,a motor driven stirrer, and an insulated spiral condenser outlet whichwas cooled at -30° C. were added2,2,8,8-tetranitro-4,6-dioxanonane-l,9-diol (DINOL, 20.0 g, 0.0581 mol),bis(2-fluoro-2,2-dinitroethyl)dichloroformal (19.31 g, 0.0496 mol) and1,2-dichloroethane (13.0 mL). A preheated 75° C. oil bath was raisedaround the flask causing the contents to form a solution quickly. Arapid, steady stream of nitrogen was passed through the solution via asintered glass sparge tube throughout the course of the reaction. Aftersix days, 98.24% of the calculated amount of hydrogen chloride had beentrapped by an aqueous sodium hydroxide solution (0.1 N). A white solidwas isolated by evaporation of the solvent under vacuum and allowing thefoam thus formed to solidify. The hydroxyl equivalent weight correctedfor the extent of reaction was 1785, measured from the decrease in theinfrared absorption of toluenesulfonylisocyanate. The number averagemolecular weight calculated from the reactant ratio corrected for theextent of reaction was 3792. Thus, the functionality was 2.12.

Example 4

The prepolymer produced in example 3 (4.00 g) dissolved inbis(2-fluoro-2,2-dinitroethyl)formal (FEFO, 4.84 g) was degassed undervacuum overnight at 60° C. Isophorone diisocyanate (0.17 g),N,N',N"-trisisocyanatohexylbiuret (0.13 g), and dibutyltin dilaurate(0,004 g) were added. The solution was degassed under vacuum for 20minutes and cured at 60° C for four days to form a clear elasticgumstock.

Example 5

2,2,8,8-tetranitro-4,6-dioxanonane-l,9-diol (60.0 g, 0.174 mol),bis(2-fluoro-2,2-dinitroethyl)dichloroformal (54.25 g, 0,139 mol), andethanol-free chloroform (51.0 mL) were added to a three-necked, roundbottomed flask equipped with a nitrogen sparge tube inlet, an insulated,spiral condenser outlet at -25° C., and a motor driven stirrer. Apreheated 60°-65° C. oil bath was raised around the flask causing thecontents to form a solution quickly. A rapid, steady 6 stream ofnitrogen was passed through the solution throughout the course of thereaction. After 25 hours, 81% of the calculated amount of hydrogenchloride had been trapped in an aqueous sodium hydroxide (0.1 N)solution. The supernatant liquid was decanted from the cooled mixture.The residue in the flask was extracted with stirring two times with 2%methanol-chloroform and two times with 100% chloroform. The remainingsolvent was removed in vacuo, and the solid foam was powdered. Yield:69.85 g (66.93% overall yield, 95.92% based on the extent of reaction).The hydroxyl equivalent weight of the material, corrected for thepresence of some (˜5-8%) nonfunctional cyclic orthocarbonate, was 998.3g/eq. OH. Analysis by gel permeation chromatography gave the followingcorrected values: weight average molecular weight of 2830, numberaverage molecular weight of 2121, and dispersity of 1.33. Thus, theaverage functionality of the chains above 1000 molecular weight is 2.12.

Example 6

The prepolymer prepared in example 5 (4.00 g) and dibutyltin dilaurate(0.04 g), dissolved in bis(2-fluoro-2,2-dinitroethyl)formal (5.55 g)were degassed under vacuum for two hours at 55° C. Toluene diisocyanate(0.27 g) and an aromatic polyfunctional isocyanate (trade name: PAPI135, Upjohn Co., 0,095 g) were added. The solution was degassed undervacuum at 55° C. for four hours and cured at ambient pressure at 55° C.for seven days with a few bubbles showing up after two days to form anelastic gumstock.

Example 7

    ______________________________________                                        DEGREE OF REACTION UNDER                                                      DIFFERENT CONDITIONS                                                          REACTION CONDITIONS      RESULTS                                                                  Tempera- Time                                             Run  Solvent*       ture     (hrs.)                                           ______________________________________                                        1    No solvent     80-85° C.                                                                       24    crosslinked                                                                   material                                   2    20% FEFO**     80° C.                                                                          25    crosslinked                                                                   material                                   3    30% to 50% FEFO                                                                              75° C.                                                                          48    incomplete                                                                    reaction                                   4.   29% CH.sub.2 ClCH.sub.2 Cl                                                                   75° C.                                                                          144   complete                                                                      reaction                                   5.   26% CH.sub.3 NO.sub.2                                                                        75° C.                                                                          60    complete                                                                      reaction                                   6.   26% CH.sub.3 NO.sub.2                                                                        85° C.                                                                          36    complete                                                                      reaction                                   7.   1,2-dimethoxy-                incomplete                                      ethane, gamma-                reaction                                        butyrolactone                                                                 BF.sub.3 ·Et.sub.2 0                                            8.   26% CH.sub.3 NO.sub.2                                                                        70° C.                                                                          72    94% complete                                                                  reaction                                   9.   26% CHCH.sub.2 CHCH.sub.2                                                                    70° C.                                                                          72    95% complete                                                                  reaction                                   10.  26% CHCH.sub.2 CHCH.sub.2                                                                    70° C.                                                                          39    complete                                        + Dinol                       reaction                                   11.  24% CHCL.sub.3 65° C.                                                                          24    67% complete                                                                  reaction                                   ______________________________________                                         *Weight percentage of solvent based on the total weight of the solvent        plus reactants                                                                **FEFO is bis(2fluoro-2,2-dinitroethyl) formal.                          

Example 8

Properties of Bis(2-fluoro-2,2-dinitroethyl)dichloroformal/dinolprepolymer

Appearance: White Powder

Melting Range: 60-100° C.

Vacuum Thermal Stability (120° C., 48 H): 1.01 cc/g

Density: 1.67 g/mL

Heat of Formation: -603.8 cal/g

Calculated Detonation Pressure (Kamlet-Jacobs): 258 Kbar

Electrostatic Senisivity: ) >12.5 joules

Sliding Friction: >980 ft-lbs

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. An energetic hydroxy-terminatedpoly(2-fluoro-2,2-dinitroethyl) polynitroorthocarbonate prepolymer ofthe formula ##STR10## wherein n>1, X is selected from the groupconsisting of F and NO₂ , and wherein when X is F, -A- is selected fromthe group consisting of --CF₂ --, --CF₂ CF₂ --, --CF₂ CF₂ CF₂ --, and--CF₂ CF₂ CF₂ CF₂ --, but when X is NO₂, -A- is selected from the groupconsisting of --CH₂ CH₂ --, --CH₂ OCH₂ --, and --CH₂ OCH₂ OCH₂ --.
 2. Anenergetic hydroxy-terminated poly(2-fluoro-2,2dinitroethyl)polynitroorthocarbonate prepolymer according to claim 1 which has anaverage molecular weight of from 1,000 to 10,000.
 3. An energetichydroxy-terminated poly(2-fluoro-2,2dinitroethyl)polynitroorthocarbonate prepolymer according to claim 1 wherein X is Fand -A- is selected from the group consisting of --CF₂ --, --CF₂ CF₂ --,--CF₂ CF₂ CF₂ --, and --CF₂ CF₂ CF₂ CF₂ --.
 4. An energetichydro-terminated poly(2-fluoro-2,2dinitroethyl) polynitroorthocarbonateprepolymer according to claim 3 wherein -A- is selected from the groupconsisting of --CF₂ --and --CF₂ CF₂ --.
 5. An energetichydroxy-terminated poly(2-fluoro-2,2dinitroethyl)polynitroorthocarbonate prepolymer according to claim 1 wherein X is NO₂and -A- is selected from the group consisting of --CH₂ CH₂ --, --CH₂OCH₂ --, and --CH₂₀ CH₂ OCH₂ --.
 6. An energetic hydroxy-terminatedpoly(2-fluoro-2,2dinitroethyl) polynitroorthocarbonate prepolymeraccording to claim 22 wherein X is NO₂ and -A- is --CH₂ OCH₂ OCH₂ --.